Conventionally, there is well known an electrically driven electric toothbrush (see Patent Documents 1 and 2). Generally, because various components such as a driving source are incorporated in the electric toothbrush, the electric toothbrush is enlarged in comparison with an ordinary toothbrush. More specifically, the electric toothbrush is configured such that a portion gripped by a hand is lengthened and thickened in comparison with the ordinary toothbrush. Thus, a distance from the portion gripped by the hand to a vicinity of a mouth is lengthened in comparison with the ordinary toothbrush. Accordingly, when toothbrushing is performed with use of the electric toothbrush, a motion area of an arm is generally widened while brushing entirely the teeth in comparison with the toothbrushing with the ordinary toothbrush. In comparison with the ordinary toothbrush, it is necessary to firmly grip a body portion of the electric toothbrush during the toothbrushing.
Because the electric toothbrush is enlarged in comparison with the ordinary toothbrush, upon brushing a back tooth, particularly in a case where a surface on a cheek side of the back tooth is brushed, it is necessary that the body portion be firmly gripped to brush the tooth while an elbow is highly raised, and the user tends to take an unusual pose. Moreover, imperfect brushing is easily caused due to this inconvenience. Particularly, when the brush abuts on the back tooth, a leading end surface of the brush and a plane in which the teeth are aligned are deviated from each other while being not parallel to each other, and there is sometimes a point on which the brush does not actually properly abut to cause imperfect brushing although a user has a sense of the brush abutting properly on the entire back tooth.